1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to apparatus for transferring electrostatic toner images to plain sheets and the like.
2. Description of the Prior Art
There has been much development any many practical applications of image forming apparatuses, such as electrostatic copying machines. An image forming apparatus initially requires the formation of a latent electrostatic image, typically by electrographic or electrophotographic means, on a photosensitive member, such as a image drum. The latent electrostatic image on the photosensitive member is subsequently developed, i.e., toned using toner particles.
In the usual case, the toned image (referred to as toner image hereinafter) may be transferred to an image receptor such as a plain paper sheet.
Various toner image transfer methods are known in the prior art. The transfer may typically be accomplished electrostatically, by means of a charge of opposite polarity to the charge on the toner particles, the former charge being used to draw the toner particles off the image drum and onto the image receptor.
The toner image transferred onto the image receptor is subsequently fused or fixed to provide enhanced durability of the toner image.
Residual toner particles which remain on the image drum during the transferring step may be cleaned off by means of a cleaning member. Further, residual charge on the image drum is removed by means of a discharging member such as a charge removing lamp, for ensuring the next formation of latent electrostatic image.
A problem typically encountered in transferring a toner image by means of the electrostatic method is the efficiency of transferring the toner image onto the image receptor. Roughly speaking, there are two types of toner particles, one made by mechanically milling a compound to fine particles and the other made by chemically dispersing a polymerized compound to fine particles. Comparing the methods, the milling method has an advantage in the cost for manufacturing. Thus, toner made by the milling method has been overwhelmingly used for electrostatic copying machines.
Recently, it has been desired to improve the quality of copies, i.e., the images produced on an image receptor. Thus, the inventor carried out tests on toners with different particle sizes, all of which were made by the milling method.